Error on async job

Question

I'm trying to create an async task that will not block the request. The user make the request, the task will start, and the controller will render "Job is running...", this is for avoid the request being blocked waiting the task to complete. Once the task is finish, it will execute the onComplete and do something with the result of that task (for example call a service that will send a mail to an user)

| Error 2014-09-16 17:38:56,721 [Actor Thread 3] ERROR gpars.LoggingPoolFactory  - Async execution error: null

The code is the following:

package testasync

import static grails.async.Promises.*

class TestController {

  def index() {
    //Create the job
    def job1 = task {
        println 'Waiting 10 seconds'
        Thread.sleep(10000)
        return 'Im done'
    }
    //On error
    job1.onError { Throwable err ->
        println "An error occured ${err.message}"
    }
    //On success
    job1.onComplete { result ->
        println "Promise returned $result"
    }
    render 'Job is running...'
  }

Complete stacktrace:

| Error 2014-09-17 10:35:24,522 [Actor Thread 3] ERROR gpars.LoggingPoolFactory  -  Async execution error: null
Message: null
   Line | Method
 ->>   72 | doCall    in org.grails.async.factory.gpars.GparsPromise$_onError_closure2
  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
  |     62 | run       in groovyx.gpars.dataflow.DataCallback$1
  |   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor
  |    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker
  ^    745 | run . . . in java.lang.Thread

Answer 1

I ended using the executor framework with the grails-executor plugin. I uploaded a very basic example here: https://github.com/agusl88/grails-async-job-queuqe

That code is using a "custom" version of the grails-executor plugin, i merged some PR's from the plugin repo and packaged as jar just for testing propuses. The repo of the plugin is this: https://github.com/basejump/grails-executor

Answer 2

I was able to get rid of this exception in a controller by removing the onComplete and onError calls. I guess the exception happens because the parent thread ended when you called render.

So your:

Promise p = task {
    complexAsyncMethodCall(); // (1) do stuff
}
.onComplete { result -> println result } // (2) on success
.onError { Throwable t -> System.err.println("Error: " + t) } // (3) on error

Becomes:

Promise p = task {
    try {
        def result = complexAsyncMethodCall(); // (1) do stuff
        println result // (2) on success
    } catch(Throwable t) {
        System.err.println("Error: " + t) // (3) on error
    }
}

This adds coupling between your work (1) and the result processing (2 and 3) but you could overcome this by writing your own Closure wrapper that takes extra Closures as arguments. Something like this:

// may not work! written off the top of my head
class ProcessableClosure<V> extends Closure<V> {
    Closure<V> work;
    Closure<?> onError;
    Closure<?> onComplete;

    @Override
    public V call(Object... args) {
        try {
            def result = work.call(args); // (1) do stuff
            onComplete.call(result); // (2) on complete
        } catch(Exception e) {
            onError.call(result); // (3) on error
        }
    }
}

That makes your code more readable:

Closure doWork = { complexAsyncMethodCall(); } // (1) do stuff
Closure printResult = { println it } // (2) on complete
Closure logError = { Throwable t -> log.error t } // (3) on error
Closure runEverythingNicely = new ProcessableClosure(work: doWork, onComplete: printResult, onError: logError)
Promise p = task { runEverythingNicely }